The 300% increase in battery life comes from tests which utilize primarily Intel's iGPU for decoding high definition video such as watching HD movies. The real world battery increase for Kaby Lake is at least in one reviewer's test 3 times that of an almost identical PC running Skylake. Unfortunately, I have lost the link, but I will post it if I can find it.
I think you're getting mixed up with the 10bit video tests mentioned, it wont decode normal HD video any differently to Skylake or Haswell